Investigate and document locking projects with the latest Python versions

[maximlt]

In anaconda/anaconda-project#398 we observed that on a Mac it's currently not possible to perform cross-platform locks targeting Linux and using the defaults channel and Python >= 3.10.

Instead of waiting for an upstream patch, we can, in theory, immediately get unblocked by locking while setting CONDA_OVERRIDE_GLIBC to a glibc version. We will have to:

• Find the version to pin, so it's compatible with the places where the code will run (i.e. GitHub ubuntu-latest runner and AE5):
  • AE5 (holoviz.dsp.anaconda.com): 2.34 (it was 2.28 on the old cluster)
  • ubuntu-latest (22.04): 2.35
  • So I'd say let's set CONDA_OVERRIDE_GLIBC="2.34"
• Update the contributor page => Instead we added the doit lock command and documented it, it sets the env var correctly.

[maximlt]

Chatted with Jean-Luc and agreed on CONDA_OVERRIDE_GLIBC="2.34". Also decided to target Python 3.11 when updating an example.